The Brewers find themselves in a situation where the value of each additional win is very high. I am not comfortable making an exact projection for wins, but I think it's safe to say that the team projects somewhere between 85-90 wins (which I will attempt to pinpoint if we get the community projections going again). They find themselves right at the peak of the win curve. Take a look at this BP piece from 2007. I'm going to go ahead and reproduce the graph here.
It's based on the value of adding 1 win to a team's projected total in a given year. It's the value of a marginal win, or the amount your team gains in value for increasing the talent level by 1 more win. The idea behind this is that it does not pay for a team to pay much to upgrade up to about 80 to 81 wins, because that team isn't going to make the playoffs anyway. From about 82 to 90 wins, there's an increasing return to each additional win added. After the 90th win, there's still a pretty strong value for each additional win, but there's still a decreasing return. Once you get to about 96 wins, there's not much point in paying to upgrade the team, because you're getting close to a lock for a playoff spot regardless.
We're right at the prime spot in this curve. It basically says that it's well worth finding even a small upgrade before the season starts when a team is in the situation the Brewers find themselves in right now. It also seeems pretty logical that the easiest spot on the roster to upgrade at would be shortstop. There's no young player to be blocked, and the options right now are a candidate for the worst regular position player in baseball, a 41 year-old shortstop, and a shortstop who has really struggled to top a .300 OBP in AAA. It's very true that this combination of players could produce something between average and replacement level-- 1 win is probably most likely if a platoon is implemented. If everybody performs great and stays healthy, they could probably muster average production, and they'd also have to use a valuable backup at second and third-- Counsell-- to get a pretty big amount of starts. If they keep Counsell as the backup at the three positions, with Betancourt as the starter, then there's a pretty big dropoff in overall production.
As a result of all this, my proposal is that the Brewers should attempt to upgrade at shortstop in any way possible. I think a good target would be Orlando Cabrera, who is 36 years old and could be projected for something like 1.5-2 WAR over full playing time, which he would not need to be counted on to play. This would allow Counsell to be the main backup at third and second while still logging plenty of time as a backup to Cabrera. Since the team would probably not be comfortable with 2 shortstops, both over 36, it seems like they'd keep either Betancourt or Cruz on the roster.
There's another economic principle that comes into play here as well: a sunk cost. Regardless of what happens this year, the Brewers owe Betancourt $3 million. This salary should have absolutely no impact on how much they decide to play him, or if they should keep him on the roster at all. They don't pay more or less, that cost is in the rearview mirror. Justifying playing him when there's a better alternative out there because of his salary is counterproductive, and could cost this team a playoff spot.
The Brewers are in a spot where every run matters. Spending $2 million to upgrade at shortstop, if it's possible, is a shrewd move even if they have to extend their budget over a point where they are comfortable going. The value of the additional win is bigger than what it will cost. Mark Attanasio would be wise to take the relatively small hit in order to get closer to that playoff spot, because it would easily be paid for in the increased revenues associated with making the playoffs (and maybe even a run beyond the divisional round).
The alternative, of course, is keeping the current roster and looking for an upgrade on the trade market in-season. This isn't the worst strategy, but it means that the impact of a superior player will have less time to take effect-- getting a 3 WAR shortstop at midseason would barely be better than signing a player like Cabrera before the season, and the cost in salary and players (probably more prospects) would likely be high. With a limited budget and willingness to trade even more young players, the best course of action for the Brewers might be to go get a shortstop right now. The team has very few weaknesses at this point, and upgrading the most glaring one would go a long way toward getting this squad into the playoffs.